A method and apparatus for forming structural articles (known as the ARMACEL process), and articles so formed, is disclosed in the applicant's international PCT patent application No. PCT/AU95/00100 entitled “A method and apparatus for forming structural articles” (WO 95/23682) and international PCT patent application No. PCT/AU96/00541 entitled “Layered Structural Article” (WO 97/09166).
These applications disclose forming structural articles from a shape defining interior member and at least one external skin in which the interior member is at least partially fluid permeable. The basic steps of the method comprise: (1) heating a thermoplastics sheet intended to form the external skin; (2) bringing the heated sheet alongside the interior member; (3) applying a fluid pressure differential between opposite surfaces of the interior member and the sheet to conform the sheet to the shape of the interior member and mutually engage same; and (4) maintaining the fluid pressure differential until the sheet has cooled. At the commencement of step (3), the headed sheet forms a seal around the periphery of the interior member which traps air between the adjacent surfaces of the sheet and the interior member. During step (3), the air trapped between the sheet and the interior member is removed by being drawn through the (at least partially fluid permeable) interior member by the pressure differential.
This method requires the interior member to inherently be at least partially fluid permeable or to be modified so as to be at least partially fluid permeable, for example by punching holes into the member. Further, fluid permeability in one direction is lost when a skin is applied to one side of the member and holes must be then placed in that skin in order to allow the application of another skin to the other side of the member.
It is an object of the present invention to provide an improved method in which the shape defining interior member does not necessarily have to be at least partially fluid permeable.